The present invention concerns an integrated circuit microwave amplifier and in particular, a monolithic microwave integrated circuit amplifier having a novel feedback network.
Monolithic microwave integrated circuits, hereinafter referred to as MMIC, are useful in mobile cellular radio and personal communication systems. Such systems require a silicon MMIC device having 50 ohm input and output impedance which can produce a power level of least +20 dBm in order to directly drive a power amplifier stage. Additionally, the device should itself be capable of being driven by a driver device with a low noise figure at high frequencies, typically 900 MHz. Such a driver may only be capable of an output power of about 1 mW (i.e., 0 dBm) due to the noise constraint. Accordingly, there is a need for a MMIC device which is characterized by greater than 20 dB gain and greater than 20 dBm output power.
Single stage amplifiers known in the art suffer from gain limitations. One approach to overcome these limitations is to employ a second stage of amplification in conjunction with a resistor-capacitor feedback combination to match the impedances of the input and output stages. A problem with this approach is that reactive elements such as capacitors may limit the useful band width of the amplifier. Accordingly, there is a need to provide a cascaded broad band amplifier with the least number of reactive feedback elements. Moreover, the requirements for monolithic implementation, small size, efficient packaging and ease of manufacture further restrict the number of capacitive elements. Therefore, there is also a need for a broadband cascaded amplifier utilizing the least number of capacitive elements.
Accordingly, it is an objective of this invention is broadband amplifier device characterized by a gain of greater than 20 dB and an output power of greater than +20 dBm, capable of being implemented in a monolithic integrated circuit.
A further object of this invention is a broadband cascaded amplifier with the least number of capacitor feedback elements to provide for broad frequency response, monolithic implementation, ease of manufacture and efficient packaging.